Fiber-reinforced ceramics in spacecrafts and aerodynes

ABSTRACT

A movable structural component for a thermomechanically stressed assembly at least partially from fiber reinforced ceramic is disclosed, wherein the movable structural component comprises at least one structural element made by an polymer infiltration and pyrolysis process and at least one structural element made by a chemical vapor process.

TECHNICAL FIELD

The present invention refers to a movable structural component for athermomechanically stressed assembly made from a fiber reinforcedceramic, particularly for reflyable aerodynes in the aviation andaerospace technique as well as a process for producing the structuralcomponent.

TECHNICAL BACKGROUND

Reflyable spacecrafts, like for example the Shuttle Orbiter, require forreentering into the atmosphere a protective shield which is, among otherthings, heat resistant. The Shuttle Orbiter of the United States ofAmerica has for this reason body and control surfaces consisting ofmetallic material which are covered with tiles from a reinforced fiberisolation. These tiles avoid the consequence that under the influence ofthe highly heated air, converted to a plasma status by the high airspeed, the metallic structural elements become so highly heated as tolose their strength and shape stability and will even be destroyed underthe load of the flight. Similar or identical problems result with anythermally highly stressed structural elements to be used in the toolmaking and engineering industry.

Assemblies, structural elements or structural parts, which are based onsubsequently disposed or glued-on isolations exhibit considerabledisadvantages as is known in the art.

For example the most highly loaded components of a reflyable spacecraft,which, in particular, are the control flaps and such control surfaces,must be made of extremely temperature resistant metallic alloys,so-called superalloys. These have a high specific gravity. Additionally,there is the weight of the thermal isolation. Very dense isolatingmaterials have to be used, to have sufficient resistance against theinfluences onto such fairings.

Despite the use of very dense fiber isolations known from the state ofthe art, a heat shield such as that of the Shuttle Orbiter, requireshigh repair and replacement work since the deposition by gluing and thelow strength of the isolating material often results in damage or evencomplete destruction under the described application conditions.Additionally, there is the weight of the thermal isolation which affectsthe total weight of the aerodyne.

OBJECT AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to overcome thementioned technical and economical problems by providing structuralcomponents which allow material and structural elements to inherentlyhave an overall increase of thermal and mechanical loading capacity. Inconnection with the construction of aerodynes, a considerable reductionin weight of the structural components and the reusability orreflyability thereof is envisaged.

The central aspect of the invention is to construct structuralcomponents, particularly for reflyable aerospacecrafts, from a fibercomposite ceramic. Thereby, depending on the mechanical and thermalrequirements to be addressed to individual elements of the structuralcomponents, differently produced materials, so called CMC-materials(Ceramic Matrix Composites), could be used.

The present invention thus provides a movable structural component for athermomechanically stressed structure, which at least partially is builtfrom a fiber reinforced ceramic. Thereby, the movable structuralcomponent comprises at least one structural element formed by a polymerinfiltration and pyrolysis process (subsequently referred to asLPI-process) and at least one structural element formed by a gaseousphase infiltration or chemical vapor infiltration process (subsequentlyreferred to as CVI-process).

With the structural components according to the invention, a 40% weightsaving as well as a significant reduction of the maintenance costscompared with the state of the art is possible. The reduction of themaintenance costs results in that the structural components according tothe invention are mechanically and thermally extremely loadable and thusfor example during the entry of the atmosphere are less damaged ordestroyed.

In accordance with the invention, fiber reinforced ceramics areconsidered for use which are based on high temperature resistant fibers.These are, particularly, carbon fibers imbedded within a matrix ofsilicon carbide (C/SiC ceramic), silicon carbide fibers imbedded withina matrix of silicon carbide (SiC/SiC ceramic) or silicon nitride(SiC/Si₃N₄-ceramic), aluminum oxide fibers imbedded within an matrix ofaluminum oxide (Al₂O₃/Al₂O₃-ceramic), mullite fibers imbedded within amullite ceramic or polyborosilazane fibers (SiBNC) imbedded within apolycarbosilane, polysilazane or silicon carbide matrix. The propertiesof these ceramic materials reinforced with filaments are mainly knownand, for example, described in A. Mühiratzer and H. Köberle in Metall(1991), page 435 cf. These materials, however, may be essentiallyinfluenced by the manner of their production and processing,respectively. A discussion of suitable fiber or ceramic materials,respectively, may be also found in “Advanced Materials 2 (1990), no. 9,pages 398-404 and “Journal of European Ceramic Society 12 (1990), pages27-41”.

In accordance with the present invention, carbon reinforced siliconcarbide ceramics (C/SiC ceramics), in particular, are envisaged, which,adapted to the final form of the structural element, are formed eithervia chemical vapor infiltration (CVI-process) or via (liquid) polymerinfiltration and pyrolysis (LPI-process). The material producibleaccording to the CVI-process is particularly suitable for mechanicallyhighly stressed parts. In case of, for example, a control flap of anaerodyne, these are the longitudinal and transversal load bearingimplements, the connecting or push-rod, the bearings and the hinges aswill be further described in detail. For mechanically or thermally lessstressed structural elements, a material produced according to theLPI-process is also suitable.

In accordance with an aspect of the invention, the structural componentis characterized in that the at least one structural element formed bythe liquid polymer infiltration and pyrolysis process is embodied as thebase of the movable structural component. These mostly large sized orvolumed bases are, in particular, mechanically less stressed so thatthey may be produced by the LPI-process.

According to another aspect of the invention, the base is a box-typesegment with a bottom wall and side walls integrally formed thereon.This measure allows for a wide variation in the final size of thestructural component and an accommodation to the individual purpose ofuse. Via the integrally formed side walls, individual box-type segmentsmay be coupled to larger structural elements or components,respectively.

In a suitable embodiment of the invention, the bottom wall, of the atleast one box-type segment, is an essentially plane surface opposite tothe side walls. This embodiment avoids the formation of so-called hotspots and along with it the premature wear of the structural element bythermal and/also or mechanical load.

Further, it is within the scope of the invention that the junctionregion between the bottom wall and the side walls is chamfered. Also,this embodiment avoids or minimizes the formation of hot spots.

According to another aspect of the invention, the at least one box-typesegment of the base is stiffened by reinforcement ribs which are, inparticular, integrally disposed on the bottom wall and the side walls.These reinforcement ribs or the like avoid torsions of the structuralelement or the structural component, respectively, under mechanicalstress and allow, in particular, a lightweight construction required forthe structural elements or structural components, respectively, like,for example, the control flaps of a reflyable aerodyne. Thesereinforcement ribs may be arranged transversally, longitudinally ordiagonally.

Furthermore, it is within the scope of the invention that the at leastone box-type segment of the base has a cover or the like, which isreversibly mountable on the side walls, thereby promoting the stiffeningof the segment and which, by its essentially plane surface, allocates amechanical stress over all the structural element.

In a further and most particularly preferred embodiment of the presentinvention, the base is composed of several box-type segments which, asalready mentioned, are connectable with each other by respectiveadjacent side walls. This allows the exchange of possibly damaged ordestroyed individual segments and, in the construction, a greatvariability with respect to the size of the structural elements orstructural components to be assembled.

Of high importance for a structural element or such a structuralcomponent, embodied according to the invention which, for example, isused as control flap for a reflyable aerodyne, several box-type segmentsare arranged side by side such that the joints between the adjacent sidewalls extend in a direction which is essentially parallel to a possiblemovement of the thermomechanically stressed assembly. This specialarrangement of the box-type segments in connection with aerodynes is notonly aerodynamically favorable but also avoids the formation of theso-called hot spots which may result in the destruction of thestructural element or of an individual segment thereof.

As mentioned above, it is within the scope of the invention that the atleast one structural element formed by a chemical vapor infiltrationprocess is embodied as a load transmission and/or bearing element of themovable structural component. The ceramics which are produced close totheir final shape by the chemical vapor infiltration process due to theincreased density have a very pure matrix with fine crystalline, densemicrostructure imparting a high thermomechanical resistance, stiffness,compressive strength and wear resistance to the material. Also the highfracture toughness of the so produced materials has to be emphasized.

Further in accordance with the invention, the load transmission and/oralso the bearing element(s) are mounted on the base of the movablestructural component for its movement.

The load transmission and bearing element comprise at least onelongitudinal beam and at least one, preferably two, transversal beamswhich are releasably mountable to each other and on the side wall of theat least one box-type segment of the base. If there is only one box-typesegment, the longitudinal and/or at least the transversal beam(s), eachextend centrally between the respective side walls.

In general the at least one longitudinal beam and the at least one,preferably two, transversal beams, are about centrally received by andarranged on the base. A highest possible stability of the structuralcomponent results from this arrangement with respect to its movementrelative to an assembly with which it is connected.

The load transmission and bearing element comprises at least one rod orthe like which transfers a force produced by a motor over the at leastlongitudinal beam and the at least one, preferably two, transversalbeams of the base of the movable structural component.

Preferably, the load transmission and bearing element further comprise abearing between the at least one beam and the at least one, preferablytwo, transversal beams as well as the at least one rod, which issemi-spherical, spherical, dome or the like shaped. During the entranceinto the atmosphere a reflyable aerodyne, particularly its controlflaps, is exposed not only to thermal but also to great mechanicalstresses which may cause lateral torsions and often even local presscompactions at the structural component or the assembly, respectively.Such lateral torsions can be received or balanced by the bearings usedaccording to the invention which are formed semi-spherical, spherical,dome or the like shaped.

The bearing therefore has preferably a semi-spherical, spherical, domeor the like shaped formed bearing shell which is supported by a bearingpin or bolt or the like on the at least one transversal beam and a meansfor receiving the bearing shell cooperating therewith which is disposedat the end side of the rod and vice versa.

For stabilization or more stable movable connection of the structuralcomponent with the assembly there is arranged preferably at least one,preferably two further bearing elements for movably connecting themovable structural component with the assembly on at least one of theside walls of the at least one box-type segment, which is/are formedparticularly like a hinge.

In a particularly suitable embodiment of the structural component of thepresent invention, at least one, preferably two of the side walls areelongated and provided with bores at its end side for receivingcorresponding bearing pins or the like of the assembly, the boring axesof which are aligned to each other or to the rotation axis of the onebearing. The boring axes thus are arranged parallel to each other or tothe rotation axis of the one bearing.

In a further preferred embodiment of the structural component of thepresent invention, the side walls and/or longitudinal beams and/ortransversal beams and/or rods are hollow sectioned. This measurepromotes the desired light construction of the overall assembly havingsimultaneously a high stiffness.

An essential feature of the present structural component is that, forincreasing its mechanical and thermal stability, coupling elements likescrews, pins, rivets and the like, formed by chemical vapor infiltrationare provided for a detachable connection of the structural elements witheach other which particularly are used in the region of the side wallsand the base. Such connecting elements naturally are exposed to highmechanical stresses and represent starting points for the formation ofhot spots. The choice of material and arrangement of the connectionelements contributes to the further stabilization of the structuralcomponents.

A further feature of the present invention is that the structuralelement for the protection and stabilization of its outer surface,particularly for protection against oxidation, is provided with asuitable protective layer, if necessary. For structural elementsproduced according to the CVI-process then at least one layer of about100 μm thickness is used which is formed essentially of the samematerial as the matrix forming material. This layer is applied bychemical vapor deposition. In the case of a C/Si ceramic, a SiC/SiCceramic or related ceramic such a protective layer is particularlyeffective if at least one boron containing silicon carbide layer isprovided. Parts without joining surfaces also may be equipped with apure silicon carbide layer onto which a multiphase cover layerconsisting of a glass matrix with imbedded refractory phases is appliedaccording to German patents P 40 34 001 and P 44 43 789.

As mentioned for several times, the aforedescribed structural componentfor a thermomechanically stressed assembly may be embodied as a movablecontrol flap or the like of an aerodyne. Particularly, reflyablespacecrafts which are exposed to high thermal and mechanical stressesduring reentrance into the atmosphere as well as control surfaces ofdiverse military missiles which receive similar stresses may exploit thestructural component according to the invention. It may be alsoenvisaged to use the structural components according to the inventionfor producing thermally and mechanically highly stressed tools andmachine parts.

The invention also refers to a process for producing the aforedescribedstructural components from a fiber reinforced ceramic for athermomechanically stressed assembly. At least one structural element isproduced by the LPI-process, at least one structural element is formedby the CVI-process and the structural elements are combined to theclaimed structural component in a suitable way.

The structural elements preferably are joined together by connectingelements, like screws, pins, bolts, rivets and the like produced by theCVI-process.

The afore-mentioned processes have different advantages which can beused in a suitable manner for the individual structural components,particularly the control flaps for reflyable spacecrafts.

In principle, for lightweight constructions the integral construction isto be preferred. The known manufacturing processes for fiber compositeceramics, however, allow this way of construction only in a limitedrange for large sized or volumed components. According to the invention,therefore, a so-called hybrid or composite construction was developed inwhich mechanically highly stressed structural elements of a structuralcomponent, for example these are with the afore mentioned control flapthe longitudinal and transversal beams (load bearing implements), therod, the bearings and the hinges, are produced by the so-calledCVI-process, particularly the gradient CVI-process. This processprovides a high performance material with respect to itsthermomechanical properties. The essential feature of these materials istheir matrix with fine crystalline, dense structure which imparts thehigh thermomechanical resistance, stiffness, pressure resistance andwear resistance to the material. Essential is also the high fracturetoughness of this material in connection with the construction ofsecurity structural members.

Structural elements which are less mechanically stressed, like thecontrol flap body of a reflyable spacecraft according to the inventionare produced according to the so-called LPI process. Generally eitherfabric cuts are disposed on molds by means of the wet laminating processor disposed dry in a forging die and filled with the matrix formingresin according to the RTM (Resin Transfer Molding) process.

According to the invention structural elements formed by the LPI-processare produced as follows: Fabric cuts from thermally highly stressablefibers are disposed on positive molds having a shape close to the endshape or into such forging dies; the disposed fabric cuts preferably areimpregnated with an organic polymer or polymer resin corresponding tothe fiber; then the material is cured under increased temperature andpressure and the so formed green compact is submitted to a pyrolysistreatment at about 900° to 1,600° C. for producing a fiber reinforcedmatrix or the desired ceramic material, respectively.

In a preferred way the curing takes place at 200° C. and at about 5 barand the pyrolysis treatment at about 1,200° C.

To protect the aforeproduced structural elements against oxidation, ifnecessary, —this is particularly required in case carbon fibers orfibers covered with pyrocarbon are used for producing the ceramic—,according to the invention, they are provided at least partly with atleast one protective layer produced by chemical vapor deposition (CVDprocess). The material forming the protective layer preferably willcorrespond to the material forming the matrix.

For producing the at least one structural element produced by chemicalvapor infiltration (CVI process), a fabric layer of thermally highlystressable fibers is at least partly and spaced apart, provided with asuitable adhesive, the fabric layer then wound up to an essentially tubeshaped fiber preform with suitable diameter, the fiber preform insertedinto a chemical vapor infiltration reactor and submitted to a gradientchemical vapor infiltration under the action of amethyltrichlorsilane/hydrogen process gas or an equivalent process gas.Details of this process can be derived from the following example.

Essentially a temperature gradient of between 700° C. inside the tubeshaped fiber preform and of about 1,150° C. in the reactor is adjusted.

The process according to the invention is characterized in thatthermally highly stressable fibers are incorporated in a respectivematrix bed which are chosen from the group of carbon, silicon carbide,aluminum oxide, mullit and/or polyborosilazane fibers.

For forming the matrix, starting materials will be chosen, whichessentially correspond to the fiber material. Preferably a C/SiC ceramicis used.

In the following, the invention will be explained in more detail bymeans of a preferred embodiment and with reference to the followingdrawings as well as to an example in which the manufacturing process forthe structural component of the present invention is given.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic perspective view of an embodiment of two movablestructural components according to the invention on a thermomechanicallystressed assembly;

FIG. 2 is a schematic perspective partially exploded view of anembodiment of a structural element of FIG. 1 according to the inventionformed by polymer infiltration and pyrolysis process in an enlargedrepresentation;

FIG. 3 is a perspective view of the embodiment of the structural elementaccording to FIG. 2 formed by polymer infiltration and pyrolysis processin assembled form, together with partially provided covers of theinvention and embodiments of structural elements according to theinvention formed by chemical vapor infiltration;

FIG. 4 is a schematic, partially exploded view of the embodiment of theinventively formed structural element of FIG. 3 without a cover;

FIG. 5 illustrates an enlarged, perspective partial view of theembodiment of one of the structural elements formed by chemical vaporinfiltration in assembled form corresponding to arrow V in FIG. 4;

FIG. 6 is a perspective view of the embodiment of the structural elementaccording to FIG. 2 formed by polymer infiltration and pyrolysis processin assembled form without the inventive cover but together with furtherembodiments of structural elements formed by chemical vaporinfiltration; and

FIG. 7 is schematic, partially broken and exploded view of the furtherembodiments of the structural elements formed by the chemical vaporinfiltration process of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 there is presented schematically an embodiment of two movablestructural components 10 of the invention for a mechanically stressedassembly 12. Here, the two movable structural components 10, forexample, are embodied as control flaps, so-called body flaps, or thelike control surfaces of a thermomechanically highly stressed assembly12. The control flaps or the like control surfaces are provided as anelevator and rudder. For controlling the pitch and wing dropping and fortrimming the angle of incidence of the assembly 12 the control flaps orthe like control surfaces are embodied movably, i.e. for examplepivotably with respect to the assembly.

As thermomechanically stressed assembly 12, aerodynes are consideredwhich both thermally and mechanically become highly stressed.Particularly, such aerodynes are reflyable spacecrafts like the ShuttleOrbiter or the Experimental Orbital Glider X-38, exemplified in FIG. 1,which are exposed to such extreme thermal and/or mechanical conditionsduring reentrance into the atmosphere. Operation temperatures of about1,000 to 2,000° C. regularly occur. Furthermore, similar loads act on,for example, military missiles.

The movable structural component 10 for a thermomechanically stressedassembly 12 which consists at least partially of fiber reinforcedceramic, comprises at least one structural element made by polymerinfiltration and pyrolysis process and at least one structural elementmade by chemical vapor infiltration. As far as possible, the movablestructural component 10 has additionally one or more structural elementswhich consist of metal or the aforementioned metal alloy.

According to FIG. 2 the at least one structural element made by polymerinfiltration and pyrolysis process is embodied as the base 14 of themovable structural component 10. The base 14 consists of at least onebox-type segment 16 having a bottom wall 18 and side walls 20, 20′, 20″,20′″ integrally formed thereon. As can be particularly derived from FIG.2, the base 14 in this embodiment is composed of several, essentiallyelongated box-type segments 16, 16′, 16′″. The box-type segments 16,16′, 16″, 16′″ are connectable by adjacent side walls 20, 20″. With suchan embodiment the torsion stiffness of the base 14 may be essentiallyincreased. On the other hand it is easily possible to disassembleindividual box-type segments 16, 16′, 16″, 16′″ for maintenance andrepair purposes, if necessary and afterwards to reassemble or tocompletely exchange them.

In a particularly advantageous way the several elongated box typesegments 16, 16′, 16″, 16′″ are arranged side by side such that thejoints 22, 22′, 22″ (see particularly FIG. 4) between the respectivelyadjacent side walls 20, 20″ extend in a direction, which is essentiallyparallel to a possible movement of the thermomechanically stressedassembly 12. In so far the joints 22, 22′, 22″ are arranged essentiallyparallel to the direction of movement or flight, respectively of theaerodyne. With such a very favorable fluidic arrangement of the joints22, 22′, 22″, flow resistances at the movable component 10 altogethermay be constructionally easily and safely avoided and therewith localoverheatings, so-called hot spots, which may form in narrow, purely heatradiating fissures.

For further improvement of the fluidic the bottom walls 18, 18′, 18″,18′″ of the box-type segments 16, 16′, 16″, 16′″ of the base 14 have asurface 24 which is opposite the side walls 20, 20′, 20″ 20′″ and inaccordance with FIG. 1 is essentially plane.

The junction area 26, 26′, 26″ 26′″ between the respective bottom wall18, 18′, 18″ 18′″ and the allocated at least peripheral side walls 20,20′, 20″, 20′″ from fluidic reasons is also chamfered. Also in this wayadditional local overheatings, so-called hot spots, are excluded.

Such a chamfering of the junction area 26, 26′, 26″, 26′″, in thisconnection, can be achieved by an integral construction or shaping ofthe respective box-type segment 16, 16′, 16″ 16′″. Also it may beconsidered to provide the respective junction area 26, 26′, 26″ 26′″ ofthe respective box-type segment 16, 16′, 16″, 16′″ with separatecorrespondingly shaped structural elements (not shown). Such structuralelements which are embodied about an angular inside are adapted to theouter contour of the respective box-type segment 16, 16′ 16″ 16′″ andoutside are provided with a chamfering of desired size and/or shape.

The box-type segments 16, 16′, 16″ 16′″ of the base 14 are stiffened byreinforcement ribs 28, or the like . The reinforcement ribs 28 therebyeach are, particularly integrally, formed with the bottom wall 18, 18′,18″ 18′″ and the side wall 20, 20′, 20″ 20′″. In the embodiment of thebox-type segments 16, 16′, 16″ 16′″ shown in FIG. 2 the reinforcementribs 28 each are arranged between opposing side walls 20 and 20″, i.e.extend essentially vertically or transversally to the joints 22, 22′,22″ However, it is also possible to arrange reinforcement ribs 28alternatively or even cumulative also in longitudinal and/or diagonaldirection for a further stiffening of the respective box-type segment16, 16′, 16″ 16′″ and thus the whole base 14.

To further stiffen the base 14 individual, preferably any of thebox-type segments 16, 16′, 16″ 16′″ may be provided with covers 30, 30′,30″ 30′″ which each are detachably fastened at the side walls 20, 20′,20″ 20′″ of each box type segment 16, 16′, 16″ 16′″. In FIG. 3 only thecovers 30″ 30′″ of the box-type segments 16″ or 16′″, respectively, areshown.

According to FIGS. 3 and 4, the at least one structural element made bychemical vapor infiltration is fashioned as a mechanically highlystressed load transmission and bearing element 32 of the movablestructural component 10. The load transmission and bearing element 32 isarranged on the base 14 of the movable structural component 10 for itsmovement, i.e. in the present embodiment for its pivoting.

As can be particularly derived from FIG. 4 the loading transmission andbearing element 32 comprises at least one longitudinal beam and at leastone, preferably two, transversal beams. The longitudinal beam 32 andtransversal beams 34 are detachably joint to each other and to the sidewalls 20, 20″ of the at least one box-type segment 16, 16′, 16″, 16′″ ofthe base 14 by for example angles or the like. In the shown embodimentthe longitudinal beam 34 and the two transversal beams 36 are receivedby and disposed on the base 14 about centrally. In so far the twotransversal beams 36 extend essentially over the two adjacent box-typesegments 16′ and 16″.

The load transmission and bearing element 32 further comprises a pushingrod 40. The rod 40 transfers a load or power produced by a not shown(servo) motor in a way known as such. This load or power is introducedfrom the rod 40 over the longitudinal beam 34 and the transversal beams36 into the side walls 20, 20″ of the two box-type segments 16′ and 16″and such to the base 14 of the movable structural component 10altogether.

According to FIG. 3 and particularly 4 the load transmission and bearingelement 32 comprises additionally a bearing 42. The bearing 42 on theone hand is arranged between the longitudinal beam 34 and the twotransversal beams 36 as well as the rod 40 on the other hand isfashioned particularly semispherical, spherical or dome-shaped and thelike. By such a semi-spherical, spherical, dome-shaped or the likeembodiment of the bearing 42 undesired transversal and torsion forcescan be cushioned and thus local press compaction can be avoided.

According to FIG. 4 the bearing 42 comprises a semi-spherical,spherical, dome-shaped or the like embodied bearing shell 44 or the likebearing ring. The bearing shell 44 is supported by a bearing pin or boltor the like bearing tube, that is received in borings at the end sidesof the longitudinal beam 34. For axially securing the bearing pin 46with the bearing shell 44 in the longitudinal beam 34 plain washers 50and lock washers 52 or the like securing means, like for exampletransversal pins, are provided on each end.

Furthermore, the bearing 42 shown in FIG. 4 comprises a bearing shellreceiving means 53 or the bearing plate cooperating with the bearingshell 44 which is arranged at the end side of the rod 40 by means ofconnecting pins or bolts 56 and/or other securing elements 58.

In FIG. 5 the particular constructive assembly of the bearing 42 isshown enlarged. By means of the semi-spherical, spherical, dome-shapedor the like shaped embodiment of the bearing shell 44 which iscooperating with a bearing shell receiving means 54 adapted thereto,occurring torsions, transversal and pitch forces between the movablestructural component 10 and the (servo)motor at the assembly 12 due toside torsions of the base 14 and the like can be reliably excluded.Along therewith local press compactions and thus temporal blockings orlasting damages, respectively of the movable structural component 10 areavoided, which possibly may again result in an immovableness of thestructural component 10.

The embodiment shown in FIGS. 6 and 7 of the movable structuralcomponent according to the invention comprises moreover at least one,preferably two, bearing elements 60. The bearing elements 60 also arestructural elements formed by chemical vapor infiltration. The bearingelements 60 are provided to ensure a certain static suspension and atthe same time a movable connection of the movable structural component10 with the assembly 12. The two bearing elements 60 are allocated to atleast one of the side walls 20′″ of the box-type segments 16, 16′, 16″,16′″ and are particularly formed like a hinge. The two bearing elements60 are identical in structure. Components corresponding to each otherthus are provided each with identical reference numbers.

The side walls 20 of the box-type segments 16 and 16″ and/or the sidewalls 20″ of the box-type segments 16′ and 16′″ each are elongated andprovided with bores 64 at the end side region 62. The bores 64 serve toreceive a corresponding bearing pin 66 or the like bearing tube, whichis also embodied preferably with a semi-spherical, spherical, dome-likeor the like shaped bearing shell 68 or the like bearing ringcorresponding to the bearing 42. In so far the bearing shell 66 isarranged on the bearing pin 66 which is received in borings 70 at theend sides of an angle rest 72. The angle rest 72 is composed of twoL-shaped plates with spacers disposed there between. To actually securethe bearing pin 66 with the bearing shell 68 in the angle rest 72securing elements 74, plain washers 76 and lock washers 78 or othersecuring elements like for example transversal pins are provided at eachof the end sides. The angle rest 72 again is secured by correspondingbearing pins 80 on a connecting support 82, which is arranged on theassembly 12.

The bore axes 84 of the bores 64 are oriented to each other or to therotation and bore axis 86 of the bearing 42 and thus all arrangedparallel.

Furthermore, the side walls 20, 20′, 20″, 20′″ and/or the longitudinalbeam 34 and/or the transversal beams 36 and/or the rod 40 are hollowprofiled for stiffening.

Preferably all of the structural elements are detachably connectable byconnecting elements 88, particularly screws or the like. The connectingelements 88 preferably are placed in the region of the side walls 20,20′, 20″, 20′″ of the box-type segments 16, 16′, 16″, 16′″ of the base14 so that sites of disturbances at the thermally highly stressedsurface 24 of the bottom wall 18, 18′, 18″, 18′″ are avoided and in sofar offset to less stressed areas.

EXAMPLE

The movable structural component of the invention may be used as acontrol flap for reflyable spacecrafts or aerodynes, respectively.Thereby reusable control flaps can be provided for the projects CrewReturn Vehicle (CRV) and Crew Transfer vehicle (CTV) and at first forthe afore test vehicle X-38 in connection with the construction andoperation of a space station.

In the following, therefore the manufacturing of a control flap for theExperimental Orbit Glider X-38 is described in an exemplifying and notlimiting way.

A control flap for X-38 is composed of the following CMC components,which depending on their function and their shape are produced by thegradient CVI-process or the LPI-process. In the example carbonreinforced silicon carbide ceramics are used as the material.

The components are represented in detail in FIGS. 2, 4 and 7.

In the manufacturing of the large box-type segments 16, 16′, 16″, 16′″for the base 14 tailored carbon fiber fabrics, the fibers of which areprovided with a layer or pyrocarbon, are led over positive molds in awet laminating process using polycarbosilane resin. A tailor anddeposition plan for fabric layers is so fashioned that the reinforcingor stiffening ribs 28 inside the box-type segments 16, 16′, 16″, 16′″are integrally, i.e. with filaments, bound to the outer surface of thebox-type segments 16, 16′, 16″, 16′″, thus to the bottom wall 18 and theside walls 20, 20′, 20″, 20′″. Also the covers 30, 30′, 30″, 30′″ whichare adapted to the size of the box-type segments 16, 16′, 16″, 16′″, areproduced by the wet laminating process.

The led box-type segments 16, 16′, 16″, 16′″ are cured at 200° C. and 5bar pressure in an autoclave, whereas the covers 30, 30′, 30″, 30′″ arecured under the same conditions in a hot press.

The so obtained green compacts products having the characteristics ofplastic composite parts are subjected to pyrolysis in a high temperatureoven under inert gas atmosphere. At a temperature of 1,200° C., thecured polycarbosilane resin is decomposed with elimination ofessentially methane, hydrogen and aromatics under formation of a solidof amorphous silicon carbide (SiC) which by the processing of thestarting resin under ambient air contains some oxygen. The formed SiCsolid encloses the fibers as a matrix material of a ceramic fibercomposite material.

The thermal resin decomposition regularly is accompanied by a decreasein mass and volume which results in the formation of fissures and poresin the solid residue. To balance this loss, as required, about fivesubsequent infiltration cycles with the polycarbosilane resin arecarried out with respective subsequent curing and pyrolysis treatments.With this procedure, components are obtained having a fiber content ofabout 43 vol. % and about 12 vol. % remaining porosity.

Thereafter the fitting surfaces for the joining of the boxes or box-typesegments 16, 16′, 16″, 16′″ and the arrangement of the covers 30, 30′,30″, 30′″ are processed by grinding and the bores for the screwedconnection are set, wherein in both cases diamond tools are used. Thecomponents then are covered with a SiC layer of 0.1 mm to 0.2 mmthickness by chemical vapor deposition, wherein the thickness of thelayer is taken into account by a respective over dimension of the boresand a dimension smaller than specified of the screw pins/bolts 88.

For the connection of the components screw bolts 88 having a shaftdiameter of about 6 mm and nuts with a corresponding inner diameter areused which are made according to German patent P 43 37 043 fromC/SiC-plates produced by the gradient CVI-process.

The components for the (pushing)rod 40, the longitudinal and transversalbeams 34, 36 for the mounting to the rear structure of the aerodyne, thehinges 60 and bearing 42 are produced by the gradient CVI-process.

Therefore, tubular fiber preforms are produced in a fabric windingprocess with slight over dimensionings with respect to the requiredfinal dimension of the prefabricated part, whereby for the binding ofthe fabric layers and for their fixation in a desired and suitabledistance a suitable adhesive is applied to the fabric. By a pyrolysistreatment at 1,000° C., the adhesive decomposes or degrades to carbonwhich in the subsequent CVI process step causes the shape and dimensionstability of the preforms.

For the box-type segments 16, 16′, 16″, 16′″ the rod 40 and the partsfor the mounting to the rear structure of the aerodynes rectangulartubes are used as preforms and for the bearing and hinges such with acircular cross section.

The fiber preforms inserted into molding flanges are introduced into thereactor of the gradient CVI-plant such that the process gas stream (heremethyltrichlorosilane [CH₃SiCl₃/hydrogen [H₂]) is fed into the inside ofthe tube and due to a sealing at the flange has to flow through thefiber wall. This causes a pressure gradient over the fiber wall. Thereactor room is heated to a uniform temperature of 1,150° C. so that theoutside of the fiber preform is also at this temperature. The inside ofthe tube contrary is kept at a lower temperature (initially about 700°C.) by means of an inserted water cooling, i.e. a defined temperaturegradient is adjusted. This temperature gradient causes that the processgas fed from the inside of the tube penetrates the fiber structure,without that a deposition of silicon carbide (SiC) occurs, because thetemperature is not sufficient for this thermally induced process. Onlyon the outer zone of the tube, being at the higher temperature, thedeposition of SiC onto the fibers occurs. By the filling of the poreswith SiC, the thermal conduction increases, whereby in the course of theinfiltration the temperature causing the SiC deposition moves throughthe whole thickness of the wall of the fiber body and thus a completematrix infiltration is achieved. The advantage of this procedure is inthe relatively short process time because due to the forced flow throughof the fiber structure a process gas pressure in the dimension ofatmospheric pressure and a high process temperature may by applied,without an early occlusion of the surface blown by the process gasoccurs.

From the so produced tube shaped C/SiC-semifinished products bearing andhinge parts 42, 60 as well as bearing boxes 16, 16′, 16″, 16′″, rods 40and beams 34, 36 are cut with coarse dimensioning. The tube parts aredimension processed by grinding with subtraction of the thickness of thelayer for the CVD-SiC-layer. Subsequently the parts are covered by theCVD process with 0.15 mm SiC and finally polished.

As a last process step, the final mounting of the parts is carried outon a dressing bench wherein a defined prestress of 3 kN is applied tothe bolts 88.

The finished control flap for example has an overall length of 1.6 m andan overall width of 1.5 m. It is about 40% more light than a usualcontrol flap of the same size produced by a superalloy and isolationtiles.

The movable structural component according to the invention is notlimited to the shown embodiment. It may by envisaged to provide forexample two load transmission and bearing elements 32 and only onebearing element 60 instead of a one load transmission and bearingelement 32 and the two bearing elements 60 to obtain a static predefinedsuspension according to the aforementioned embodiment. Simultaneously itcould be possible to offset the two transmission and bearing elements 32from the center of the base 14 to its corners and the bearing element 60to about the center of the side wall 20′″ of the box-type segments 16,16′, 16″, 16′″ of the base 14.

Furthermore, it is possible to plan a kinematic reversal with respect tothe arrangement of the bearing bolt 46 with the bearing shell 44 as wellas the bearing shell receiving means 54 of the bearing 42 or the bearingpin 66 with the bearing shell 68 and the bores of the bearing element60. This then could result in that the bearing 42 is embodied to becomparable with both bearing elements 60 and vice versa.

Finally, it is possible that individual parts of the structuralcomponent 10 and/or the assembly 12 consist in an alternative orcumulative embodiment at least partially of metal, a metal alloy or thelike as for example the longitudinal beam 34 and the two transversalbeams 36.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. A movable control surface for athermomechanically stressed aerodyne or spacecraft the movable controlsurface comprising: a moveable base made of fiber reinforced ceramicmade by a polymer infiltration and pyrolysis process; a moveable controlmember of fiber reinforced ceramic made by a chemical vapor infiltrationprocess connected to said base.
 2. The movable control surface of claim1, wherein the base part includes at least one box-type segment having abottom wall and side walls integrally formed thereon.
 3. The movablecontrol surface of claim 2, wherein the bottom wall of the at least onebox-type segment has an essentially planar surface opposite the sidewalls.
 4. The movable control surface of claim 2, wherein a transitionregion between the bottom wall and the side walls is chamfered.
 5. Themovable control surface of claim 2, wherein the at least one box-typesegment of the base is stiffened by reinforcement ribs particularlyintegrally formed on the bottom wall and the side walls.
 6. The movablecontrol surface of claim 2, wherein the at least one box-type segment ofthe base part is stiffened by a cover, detachably mounted on the sidewalls.
 7. The movable control surface of claim 2, wherein the base partconsists of several box-type segments, which are connectable byrespectively adjacent side walls.
 8. The movable control surface ofclaim 6, wherein the several box-type segments are arranged side by sidesuch that the joints between the respectively adjacent side walls extendin a direction essentially parallel to a possible movement of thethermomechanically stressed assembly.
 9. The movable control surface ofclaim 1, wherein the load transmission or bearing element includes asection for connecting with said control surface.
 10. The movablecontrol surface of claim 1, wherein the movable control member includesload transmission or bearing elements comprising at least onelongitudinal beam and at least one transversal beam which are detachablymountable to each other and to the side walls of the at least onebox-type segment of the base.
 11. The movable control surface of claim10, having two transversal beams.
 12. The movable control surface ofclaim 10, wherein the at least one longitudinal beam and the at leastone transversal beam are about centrally received by and arranged on thebase.
 13. The movable control surface of claim 10, wherein the loadtransmission and bearing element comprises at least one rod whichtransfers the force produced by a motor via the at least onelongitudinal beam and the at least one transversal beams onto the baseof the movable structural component.
 14. The movable control surface ofclaim 10, wherein the load transmission and bearing element comprises abearing, arranged between the at least one longitudinal beam as well asthe at least one rod and is particularly one of semi-spherical,spherical and dome-shaped.
 15. The movable control surface of claim 14,wherein the bearing comprises a one of semi-spherical, spherical adome-shaped bearing shell which is supported by a bearing pin on the atleast one longitudinal beam and a bearing shell receiving devicecooperating with the bearing shell which is arranged at the end side ofthe rod.
 16. The movable control surface of claim 10, having two bearingelements.
 17. The movable control surface of claim 10, wherein at leastone of the side walls are elongated and at the end side portion providedwith bores for receiving corresponding bearing bolts of the assembly,the boring axes of which being oriented to each other or to the rotationaxis or the one bearing, respectively.
 18. The movable control surfaceof claim 2, wherein the side walls or longitudinal beam or transversalbeam or rod is hollow profiled.
 19. The structural component of claim 1,wherein the structural elements of connecting elements made by chemicalvapor infiltration process, particularly screws, are detachablyconnectable with each other, which are arranged particularly in theportion of the side walls of the base.
 20. The structural component ofclaim 1, wherein the structural elements are provided with a protectivelayer for protecting the ceramic from oxidation.
 21. The control surfaceof claim 1, wherein the movable control surface is embodied as a movablecontrol flap of an aerodyne or spacecraft.